The various mechanisms which are potentially capable of contributing to overall regulation of cardiovascular function during arterial hypoxia, such as chemoreceptor reflexes, central nervous influences, cardiac output and peripheral vasoconstriction and vasodilation have been studied in isolation and are relatively clearly defined. However, the extent to which these factors interact to control the distribution of tissue perfusion to the various parallel vascular circuits has received little attention. We have developed an awake instrumented dog preparation in which it is possible to repetitively standardize regional blood flow responses to arterial hypoxia with and without chemoreceptor control of the circulation. We intend to continue our studies of regional blood flow, coronary flow and cardiac dynamics and pulmonary hemodynamics in these animals before and following chemoreceptor denervation. We further intend to explore the influence of secondary factors, such as hypocapnia and reflex influences from lung inflation on these regional hemodynamic responses and to ascertain the efferent autonomic pathways involved in the peripheral flow adjustments. The objective is to delineate the relative roles and interactive relationships of neural and local vascular mechanisms concerned in overall regulation of the circulation during systemic hypoxia. We will conduct parallel studies to those proposed above in awake animals exposed to another type of standardized environmental stress, muscular exercise, to explore the role of the sinoaortic reflexes in circulatory control during exertion. Our goal is to rigorously exploit our awake animal preparation using computerized data analysis to accurately define dynamic and steady state responses and to treat the data in terms of systems analysis to arrive at a quantitative understanding of circulatory control during standardized stress situations. BIBLIOGRAPHIC REFERENCES: Krasney, J. A. and R. C. Koehler. Heart rate and rhythm and intracranial pressure. Am. J. Physiol. 230: 1695-1700, 1976. Newell, J. C., M. G. Levitzky, J. A. Krasney and R. E. Dutton, Jr. Phasic reflux of pulmonary blood flow in atelectasis: influence of systemic P02. J. Appl. Physiol. 40: 883-888, 1976.